EP 0 838 928 A2 describes an apparatus for receiving digital signals transmitted over a transmissive channel as a sequence of OFDM multi-carrier symbols. Thereby, the transmitted signal is of the type including a reference symbol transmitted at each predetermined group of OFDM symbols. The apparatus known comprises means for generating an estimate of a channel transfer function by dividing the demodulated elementary components of a previously received OFDM symbol by the respective estimates of the same previously transmitted symbol, as obtained after equalization, forward error correction, re-encoding and re-mapping. Further, the initial estimate of the channel transfer function is obtained by dividing the demodulated components of a predetermined OFDM reference symbol by the respective components of the same transmitted symbol as stored in the receiver. The known apparatus comprises a frequency-domain filter for filtering the estimates of the channel transfer function with an equivalent “bandwidth” that is greater than the time duration of the guard interval but smaller than the time distance between the periodical repetitions of the channel impulse response due to sub-sampling in the frequency domain.
The apparatus known from EP 0 838 928 A2 has the disadvantage of a complex implementation having a very long feedback loop through the Viterbi decoder into the channel estimation. Further, the quality of the signal received may degrade for channels with fast changing impulse responses.